In microelectronics, disilane is used for deposition of silicon layers, and this has to meet ultrahigh purity demands. However, the only processes known to date use catalysts. For instance, JP 02-184513 discloses a process for preparing disilane using organometallic catalysts based on platinum, rhodium or ruthenium complex catalysts having organic phosphorus, arsenic or antimony ligands. These catalysts contribute to contamination in the ppb range of the disilane prepared and the disposal thereof is being viewed increasingly critically.
WO 2008/098640 A2 discloses a process for preparing hexachlorodisilane, which can be hydrogenated catalytically to disilane in a second process step. This two-stage process is unsuitable for the inexpensive preparation of high-purity disilane.
DE 36 39 202 discloses a further process for preparing disilane having the disadvantage of formation of significant amounts of elemental silicon during the preparation of disilane. The reactor can only be operated batchwise in this process and has to be cleaned in a costly and inconvenient manner after very short production times. A further disadvantage lies in the high yield losses which arise firstly through the silicon deposition and secondly through losses of disilane or trisilane because of stripping effects in the removal of hydrogen from the reaction products. These yield losses can be avoided in the case of synthesis via hexachlorodisilane, but the catalytic hydrogenation in turn results in contamination of the disilane and trisilane. The problem addressed by the present invention was that of providing a process and a plant which avoids the disadvantages of the prior art mentioned and preferably allows a continuous preparation of polysilanes. In addition, it was to be possible to isolate the polysilanes, even as a mixture, in high to ultrahigh purity. Preferably, a separation of the polysilanes was merely to serve the purpose of increasing the content of the pure polysilanes and not for the primary purpose of purification. An additional problem was that of providing a particularly economically viable process on the industrial scale.
These problems are solved by the process according to the invention and by the plant according to the invention.
It has been found that, surprisingly, for selective preparation of polysilanes, it is possible to utilize gas phase treatments of a stream of reactants comprising monosilane with a defined partial monosilane pressure in the gas mixture in the presence of hydrogen in nonthermal plasmas at temperatures below 40° C. and preferably reduced pressure.